About 10,000 young Jews from 29 countries will enjoy a generous gift this winter: a vacation to Israel - with the Israeli government and Jewish philanthropies picking up the tab for transportation, food, and lodging.

Those who fund the trips say the opportunity to experience Israel is the birthright of every Jew. But to donors' chagrin, handfuls of young activists have used the trips in recent years to volunteer for pro-Palestinian organizations in the West Bank - some of which directly oppose the Israeli government and Zionist ideology.

The small movement has some in the Jewish community wondering whether the Taglit-birthright Israel program is being hijacked. But as the Holocaust shifts from memory to history, it also points to efforts of young diasporal Jews to define their own ideologies, symbols, and institutions within a religious tradition that has long been at the forefront of social change.

"They have the right to explore" all sides of the Palestinian-Israeli conflict, but not using the money given "to explore certain values," says Allyson Taylor, with the American Jewish Congress's Western Region. "You have the right to buy a movie ticket, but do you sneak into another theater to see a different movie?"

While some American Jews say the issue is much ado about nothing, others see a premeditated attempt to defraud the Israeli government and Zionist advocacy groups. Some young Jewish leftists, meanwhile, say volunteering in the occupied territories is in keeping with the goals of Taglit-birthright Israel: It is an essential part of their Israel experience.

"For me, being a Jewish person means supporting social justice. For me, being Jewish doesn't mean supporting Israel," says Jessica, who traveled to Israel with Shorashim, a Birthright travel organizer, during the summer of 2004. "The lessons of the Holocaust and the lessons of Jewish history mean we need to stand up for people's rights. Otherwise, who's going to stand up for us?" Jessica asked that her last name not be used so as not to jeopardize her work on behalf of Palestinians.

Since Taglit-birthright Israel's inception in 1999, it has provided 10-day trips for some 88,000 young people - any Jew aged 18 to 26 who has never been to Israel with a guided group. The goal, say organizers, is to strengthen the commitment of a new generation of Jews to the world's only Jewish state. As for the number who volunteer for pro-Palestinian activist organizations while abroad, some say only half a dozen while others cite growing ranks of activists trained to exploit the program's generosity.

Taglit-birthright Israel declined to comment for this article.

Among pro-Palestinian organizations aided by non-Israeli Jewish activists - including an unknown number of former Taglit-birthright volunteers - is the International Solidarity Movement (ISM). The organization, according to its website, is "committed to resisting the Israeli occupation of Palestinian land using nonviolent, direct-action methods and principles." The Israeli government, though, accuses it of supporting terrorism. Since the group's founding in 2001, several activists have been killed or injured while participating in ISM protests and nonviolent resistance efforts.

"If you go to an organization like ISM, which clearly advocates suicide bombers and things like that, I would say it's not a very honest way of using this program," says Meir Shlomo, Israel's consul general to New England.

ISM advocates an end to Israel's occupation of Palestinian territories, says cofounder Huwaida Arraf. But members deny that ISM endorses violence or supports political terror. Beyond that, says Ms. Arraf, ISM does not specifically encourage its Jewish volunteers, which she estimates make up about 25 percent of the group's staff, to travel for free via Taglit-birthright.

"Birthright Israel does nothing to expose these students to the occupation that the Palestinians are living through," says Arraf. "To ... take the initiative to see more than what the Birthright organizers want them to see - we guarantee their lives will be changed."

Last summer, this reaction to the Taglit-birthright program became more institutionalized. Birthright Unplugged, a group that gives guided tours of the West Bank, offers "an educational project that primarily seeks to expose young Jewish people to the realities of Palestinian life under occupation," its website states. By design, the six-day Unplugged tours coincide with Taglit-birthright Israel's programs. Geographically, chronologically, and ideologically, Birthright Unplugged picks up where Taglit-birthright leaves off.

Last year Taglit-birthright Israel filed a "cease and desist" complaint for trademark infringement against Birthright Unplugged and charged it with "unfair competition." A lawsuit is pending.

For the many Taglit-birthright participants who don't volunteer in the West Bank, their peers' actions can elicit feelings of betrayal.

Catherine Heffernan, a Birthright participant who attended Shorashim with Jessica in 2004, felt outraged. "Whatever respect I ever had for you and your beliefs is gone," she fired off in an e-mail last summer after learning how Jessica had spent her remaining time in Israel.

But even Ms. Heffernan, who considers herself a "peaceful Zionist," says Judaism is what has informed Jessica's misguided struggle for social justice. "Jessica ... [has] a desire to see justice done in the region, and that is something [she has] learned through [her] Judaism," says Heffernan. "It seems that it is very politically savvy to be anti-Israel, and Israel has a lot of problems. I don't think that should mean joining an organization that hurts Israel."